Equipment and method in a twin-wire former

ABSTRACT

The invention concerns an equipment and a method in a twin-wire former, in which a partly pre-drained or non-drained fiber stock is passed to between the forming wires of the web former in the vicinity of the former roll ( 11 ) or of a water drain box, in which connection water is drained out of the stock web by means of the former roll ( 11 ) or the water drain box. The twin-wire former comprises a rib ( 20 ) in connection with the former roll ( 11 ) or the water drain box in the lateral area of the wires (H 2 ), which rib has been fitted to control the running of the second forming wire H 2 ) passed from the gap roll. By means of the rib ( 20 ), in the lateral area of the wire runs, the point at which said forming wire (H 2 ) reaches contact with the first forming wire in connection with the former roll ( 11 ) or the water drain box is shifted further away in the machine direction. The rib ( 20 ) is an oblong structure, which has a maximal height (H max ) in the middle area of the rib ( 20 ).

FIELD OF THE INVENTION

The invention concerns an equipment and a method in a twin-wire formerof a board machine or of a paper machine in view of controlling the edgeeffect.

BACKGROUND OF THE INVENTION

In gap formers, the web is formed by, out of the headbox, feeding afibrous stock into a gap formed by two wires. The gap formed by thewires is substantially wider than the slice jet discharged from theheadbox. When the jet arrives in the gap, the wires are placed apartfrom each other in the area of the jet, but the wires tend to enter intocontact with each other as the draining proceeds in the lateral areas.In the lateral area, in the cross direction, the thickness of the jetdoes not go to zero steeply, but gently (FIG. 1B), When the web is beingformed, water is drained out of it by the effect of pressure p=T/R. Inthe initial stage, when a fibrous mat has not yet been formed to asignificant extent, the rate of draining of water is considerable. Inthis connection, the draining of water takes place in the direction ofthickness of the web. When a fibrous mat is formed, the rate of drainingbecomes slower. In such a case, the flow in the lateral area of the jettends to turn towards the side owing to the reduction of thecross-directional face defined by the wires. The flow can take placeeither inwards or outwards. As a result of this, great divergencies froma machine-direction fibre orientation can be seen clearly in the lateralarea. This comes out in particular when large slice openings and poorlydrainable stock grades are used.

The present invention concerns a method for control and elimination ofthe detrimental edge effect in a twin-wire web former and in particularin a gap former. The method can also be used for regulation oforientation angles and basis weights in the lateral areas of the stockweb, and, thus, it is also suitable for a method of regulation of thecross-direction profiles of the web.

In Fourdrinier machines, at the edges of the web, deckle boards and edgeraising means are employed in order that the stock suspension should notflow over the edge of the wire. In gap formers, such devices for thelateral areas have not been needed, because, typically, small sliceopenings and/or quickly draining stocks have been used. But the problemof the lateral area is also present in gap formers. It is a featurecommon of Fourdrinier and gap concepts that, when the slice openings atthe headbox become larger, the problems in the lateral areas areemphasized.

Figure 1A is a side view of the slice jet and the initial draining areain a gap former. The covering wire has been illustrated to be straightand tangential to both rolls in the figure, and right at the edge of thewire, where there is no stock web between the wires, the situation isindeed similar to what is shown. FIG. 1B is a sectional view taken alongthe line I—I in FIG. 1A. It is seen from the figure that at the edgesthe covering wire and the lower wire are in contact with one another. Inthe middle area of the stock web, the covering wire and the lower wireare placed apart from one another, because the web is between them.Between the middle area and the wire edges, there is an area in whichthe wires approach each other. The edge of the stock web is placed inthis area.

Since the. edge effect described above is emphasized in the area inwhich the draining of water and the web formation have proceeded ratherfar, it affects the properties of the fibre mat that is formed. At theedges of the web the basis weight is lower than in the middle of theweb. Also, the orientation angles are different in the lateral areas ofthe web, as compared with the middle. True enough, the edges of the webare trimmed off in a later stage of the process, but, when a large sliceopening is used, the effects of the edge effect extend to a portion ofthe web that is not trimmed off. On the other hand, the smaller theportion that is trimmed off, the more cost- efficient can the process bemade.

OBJECTS AND SUMMARY OF THE INVENTION

As a solution for the problem described above, a method is described bywhose means the covering wire is raised apart from the lower wire, and,at the same time, carriage of the stock suspension away from between thewires over the web edges is prevented.

In accordance with the invention, in view of minimizing and controllingthe effects of the edge effect, in the present patent application, it issuggested that, in the twin-wire area, an arrangement of equipment inparticular connected with the former roll be employed, by means of whicharrangement the point of coming together of the forming wires in theedge area is transferred further on the former roll, i.e. in the presentinvention the area of draining is extended in which the webs are stillplaced apart from one another. Thus, when the wires reach contact witheach other, the web has already had time to be drained enough in theedge area, and, thus, no problems of fibre orientation or basis weightoccur.

In the present patent application, it is suggested that such anarrangement of equipment be employed in which a rib extending to thelateral area of the web is used. The position of the rib can beregulated by means of adjustment devices both in the machine directionand in the cross direction of the machine. In this way it is possible toregulate the position of the rib in relation to the former roll, and,thus, it is possible to regulate a controlled reaching of contactbetween the wires.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following with reference to somepreferred embodiments of the invention, the invention being, however,not supposed to be confined to said embodiments alone.

FIG. 1A illustrates the target area of the present invention inconnection with the former roll of a gap former.

FIG. 1B is a sectional view taken along the line I—I in FIG. 1A.

FIG. 1C illustrates the running of the wires H₁ and H₂ in a prior-artconstruction.

FIG. 2A illustrates the solution in accordance with the invention forthe problem illustrated in FIGS. 1A and IB. FIG. 2A shows a rib inaccordance with the invention to be fitted at an edge of the machine.The illustration is axonometric.

FIG. 2B shows a second embodiment of the rib in accordance with theinvention, in which the rib becomes narrower when proceeding in themachine direction from the headbox.

FIG. 2C illustrates a solution of regulation of the rib. The rib can beregulated and positioned both in the running direction of the wire andin the cross direction.

FIG. 2D illustrates a solution for regulation of the position of the rib20 both in the machine direction and in the cross direction in view ofregulation of the position of the rib.

FIG. 2E shows an embodiment of the invention in which the rib has beenmade of lamellae, an actuator, favourably a pneumatic hose, being fittedin the space between said lamellae so as to regulate the shape of theheight profile of the rib as desired.

FIG. 2F shows an embodiment of the invention in which the side face 20 bof the rib can be positioned by means of an actuator, favourably aloading hose.

FIG. 3 shows a former construction with which the guide in accordancewith the invention and connected with the former roll has beenconnected.

FIG. 4A shows a solution of equipment in accordance with the inventionin connection with a former roll. The illustration is from the area B₂in FIG. 3.

FIG. 4B is a sectional view of the equipment taken along the line II—IIin FIG. 4A.

FIG. 4C illustrates the area B₃ from FIG. 4B in an enlarged scale.

FIG. 4D illustrates the area B₃ from FIG. 4A in an enlarged scale.

FIG. 5A illustrates the use of an equipment in accordance with theinvention in connection with a water drain box (110).

FIG. 5B is a sectional view taken along the line III—III in FIG. 5A.

FIG. 6A illustrates the use of a rib in accordance with the invention inconnection with a twin-wire web former of a different type.

FIG. 6B is a sectional view taken along the line-IV—IV in FIG. 6A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates the target area of the invention in connection withthe former roll 11 and the gap roll 12 in a twin-wire web former 10 in aboard machine or paper machine. The twin-wire former in the embodimentshown in the figure is a gap former. The first, forming wire H₁ runs onthe face of the former roll, and the second forming wire H₂, i.e. thecovering wire, is guided onto the face of the former roll from the gaproll 12 or reversing roll. The wires H₁, H₂ reach contact with eachother in the area B. in the way shown in FIG. 1A. The stock jet W ispassed into the gap between the forming wires H₁ and H₂ in the way shownin FIG. 1A.

In a twin-wire former, such as a gap former, the web is formed so thatfibrous stock is fed from the headbox into a gap formed by two wires.The gap formed by the wires is substantially wider than the slice jetdischarged from the headbox. In the initial stage, when a fibre mat hasnot yet been formed to a significant extent, the rate of draining ofwater caused by the dynamic pressure is considerable. At this stage, nodetrimental transverse flows arise as yet. When proceeding in themachine direction, with the exception of the lateral areas, the wiresare placed apart from each other at a distance determined by thethickness of the fibre mat. In the lateral areas the wires attempt toreach contact with each other by the effect of the tension of the wire.When running with large slice openings, it is also necessary to-pressthe edges into contact with each other by means of separate sealingmembers. When a fibre mat is formed, the rate of draining of waterbecomes lower. In such a case, the flow in the lateral area tends toturn towards the middle of the web, owing to the reduction of thecross-sectional area formed by the wires. As a result of this, greatdivergencies from a machine-direction fibre orientation can be seenclearly in the lateral area. This comes out in particular when largeslice openings and poorly drainable stock grades are used. The essentialfeatures in what has been stated above are: A divergence of orientationfrom the machine direction occurs when the slice opening becomes larger,and a divergence of orientation arises at the earliest at a point atwhich a dewatering pressure has been formed inside the web. Duringinitial dewatering, no pressure occurs, because of the low resistance todraining. Nor do cross-direction flows arise to a significant extent ina later stage if the rate of draining of water out of the web issufficiently high. This can be concerned with low basis weights and withrapidly draining stock grades.

FIG. 1B illustrates the problem that occurs in a prior-art solution witha large slice opening. The figure illustrates a lateral area of the webat which the variation of the orientation angle is large. Said problemdoes not occur with small slice openings of the headbox.

FIG. 1B is a sectional view taken along the line I—I in FIG. 1A. As isshown in FIG. 1B, the stock suspension remains in the area between theforming wires H₁ and H₂ also without separate edge guides or edgelimiters, because the wires H₁ and H₂ reach contact with each other atthe edges. However, said area of contact B₁ between the wires H₁ and H₂in FIG. 1A causes problems. If the stock has not had time to be drainedadequately in said lateral areas, the fibres tend to be orienteddetrimentally away from the machine direction, owing to the change inthe area between the wires. In order to avoid said edge effect, in thepresent patent application it is suggested that an arrangement be usedin which. the covering wire is guided by means of a separate rib placedat the edge into connection with the forming wire H₁ so that thedraining area in connection with the former roll is increased and, thus,the point of contact between the wires is shifted in the lateral areasfurther in the machine direction. By means of said arrangement, thestock has had time to be drained and, thus, when the wires reach contactwith each other, corresponding faults of alignment do not arise in thefibre orientation, nor are detrimental great divergencies then noticedin the basis weight of the web in the direction of width of the machine.

FIG. 1C illustrates the running, of the wires H₁ and H₂ in connectionwith the former roll in a gap former.

FIG. 2A illustrates a. solution in accordance with the invention. Theproblem mentioned above can be solved as follows. It is essential that,after formation of a drainage pressure, attempts are made to keep thedistance between the wires in the lateral area equal to the thickness ofthe web that has been formed. This can be accomplished as follows. Tothe area of the gap, between the wires, at the edges, a rib 20 is added,which becomes thicker in the initial part when proceeding in the machinedirection, and which becomes thinner after the thickest portion. This isto say that the middle portion of the rib 20 is substantially thickerthan the initial end and the final end. The piece must be thin in theinitial stage in order that the running of the wires H₁ and H₂ shouldnot be hampered or cause significant wear both in the wire and in thepiece itself. Of course, the initial stage does, however, not affect theformation of the fault in the orientation. The thickest portion of therib 20 must be placed approximately at the point at which a drainagepressure has been formed. After this the rib 20 becomes thinner roughlyin compliance with the rate at which the web becomes thinner. The ribmust extend in the machine direction far enough in the running directionof the wire so that a possible transverse flow can no longer positionthe fibres. The thickness of the thickest portion of the rib 20 ispreferably 5 to 30 mm. The thickness of both ends of the rib 20 is 1 to5 mm. The position of the rib 20 can be regulated both in the crossdirection of the machine and in the horizontal direction. Optimally, thedistance of the side edge of the rib in the cross direction is −50 mm to+50 mm in relation to the edge of the slice jet, i.e. to the nearestedge of the piece concerned. When the distance is altered, the fibreorientation can be affected. The inlet end of the rib 20 is denoted withHin. The position of maximal height of the rib is denoted with H_(max),and the outlet end of the rib is denoted with H_(out). The inlet endrefers to the point at which the wire arrives at the rib, and the outletend refers to the point at which the wire departs from the rib.

In the equipment, the position in the running direction of the wires issuch that the starting point of the rib is at the earliest in the areaB₁ in which the wires reach contact with each other, and the final pointis at the latest where the thickness of the web is less than 1 mm.

In accordance with the invention, when the rib is formed in the waydescribed herein, a smooth introduction of the covering wire intoconnection with the rib is permitted, and a necessary drainage areadetermined by the rib height is formed in the middle area of the rib,from where the rib height is reduced to the minimum H_(out). The curveradius of the bottom face of the rib 20 corresponds to the curve radiusR of the former roll when the water drain unit is a former roll 11.

The position of maximal height H_(max) of the rib is placed in themiddle area of the rib. In such a case, it is placed in the area betweenthe inlet end H_(in), of the rib 20 in and the outlet end H_(out), ofthe rib, in which connection the thickness of the rib increases whenproceeding from the inlet end H_(in) of the rib to the position ofmaximal height H_(max) of the rib, and the thickness of the rib becomessmaller when proceeding from the position of maximal height H_(max) ofthe rib to the outlet end H_(out) of the rib.

The rib 20 is made of a wear-resistant material of low friction, such asHDPE or a metal.

A rib 20 in accordance with the invention can be used, in general, inconnection with twin-wire web formers in board or paper machines. Insuch a case, the stock suspension W is passed after the headbox 100 ofthe board or paper machine into the gap between the forming wires H₁, H₂a water drain unit, such as a former roll or a water drain box, beingplaced in the vicinity of said gap. The ribs 20 are fitted both lateralareas between the forming wires H₁, H₂. The invention is suitable forapplication in particular in connection with a gap former, whichcomprises a former roll or, in stead of a former roll, a water drainbox, such as a ribbed box or a suction box. The invention is also wellsuited for application in connection with a what is called hybridformer, in which, before the gap between forming wires, there is a whatis called water pre-drain unit in connection with one of the formingwires, which pre-drain unit is favourably a water drain box.

In FIG. 2B, the rib 20 has been shaped so that the distance of theinside edge of the rib 20 from the wire edge becomes shorter whenproceeding in the machine direction, in which connection wire is exposedon which no fibre mat has been formed as yet. Owing to reducedresistance to draining of water, the flow attempts to flow in thisdirection. The pieces can be turned to a certain angle in relation tothe machine direction. When the final end is turned outwards, wire isexposed on which no fibre mat has been formed. In such a case, the flowattempts to flow towards the edge of the web because of the reducedresistance to draining of water. The fibre orientation can be influencedby means of the magnitude of this turning.

Within the scope of the invention, an embodiment is possible in whichthe rib 20 becomes wider in the machine direction. In such a case, thefibre orientation angle is affected in the opposite direction.

As is shown in FIG. 2C, the rib 20 can also be shifted both in themachine direction and in the cross direction of the machine, in whichcase it is possible to set the location of the thickest portion of therib 20. This is done because, depending on the stock grade and on theslice opening, the place of formation of the water drain pressure variesin the machine direction. The figure shows an embodiment in which therib 20 comprises an opening 20 d in its edge 20 c, through which openinga fastening screw R5 has been passed. The opening 20 d has been madewide in relation to the diameter of the screw R5, in which case the rib20 can be adjusted both in the running direction of the forming wire inthe paper or board machine and also in the direction transverse to therunning direction of the wire.

FIG. 2D shows an embodiment of regulation, in. which the screw R6 hasbeen passed into the rib 20 through a cross-direction hole 20 e in theedge 20 c.The screw R6 has been connected to a base plate 20 f, whichcomprises openings 20 g placed in the running direction of the wire,through which opening the screws R7 connected to the machine. frame havebeen passed. In this way the rib 20 can be regulated both in the runningdirection of the wire and in the direction transverse to the runningdirection of the wire.

As is illustrated in FIG. 2E, the thickness of the rib 20 can beregulated, for example, by means of pneumatic loading or water, loadingby means of an actuator 70, such as a loading hose. The rib 20 can alsobe made of a resilient material, in which case it can also be regulatedby compressing. The rib 20 can also consist of lamellae S₁, S₂displaceable in relation to one another, in the way shown in FIG. 2E.

The actuator 70 can be a loading hose which is composed of componenthoses, in which case, by means of said actuator, the position of themaximal height H_(max) of the rib can be altered over the length of therib. At the same time, said height H_(max) can also be altered bychoosing the pressure in the loading hose appropriately.

FIG. 2F is an illustration of principle of the regulation of a resilientrib 20 in the cross direction of a board or, paper machine by means ofan actuator 700. The actuator is a loading hose. The springs J₁,J₂ . . .produce a counter force for the loading hose. The rib 20 may consist oflamellae S₁ and S₂ In the embodiments shown in FIGS. 2D and 2E, theactuator 70 and 700 is a loading hose, for example, filled withcompressed air or with a liquid. In stead of a loading hose, it is alsopossible to use other actuators, such as hydraulic cylinders, anelectric actuator, etc. When actuators are employed, they can bedistributed over the length of the rib so that, by their means, thefaces 20 a and 20 b of the rib can be given the desired curveform/position, and in this way it is possible to shift the position ofmaximal height H_(max) of the rib in the desired way in compliance witheach run.

FIG. 3 shows a gap former 10 of a board or paper machine, which formercomprises a guide 20 in accordance with the invention in connection withthe former roll. The illustration is a side view. As is shown in thefigure, the gap former 10 comprises a first forming wire H₁, which hasbeen passed over reversing rolls and guide rolls e₁, e₂ . . . and overthe former roll 11, as well as a second forming wire H₂, i.e. a coveringwire, which has been passed over reversing rolls t₁, t₂ . . . and overthe gap roll 12. The forming wire H₂, which is also called coveringwire, has been passed from the gap roll 12 into connection with thefirst forming wire H₁ guided on the former roll. Thus, over a certaindistance, the forming wire H₁ and the covering wire H₂ have a joint runon the face of the former roll 11. From the headbox 100, a stock jet ispassed into the gap between the wires H₁ and H₂. The water drain unitsare denoted with the reference numerals 50 a ₁, 50 a ₂, 50 a ₃, and 50 a₄. In an embodiment of the present invention, the former roll 11 maycomprise inner vacuum zones or suction zones or one suction zone, inwhich case water is drained out of the stock web on the suction zone andthrough the perforation in the former roll. The former roll can also bea perforated roll which does not include an inside suction box. Inaccordance with the invention, there is a rib 20 in accordance with theinvention connected to the axle of the former roll, which rib comprisesa support arm 21, with which the rib 20 is connected through a fasteningframe 23. By means of the rib, the arrival of the forming wire H₂, i.e.of the covering wire, into connection with the forming wire proper H₁running on the former roll 11 is regulated.

By means of the rib 20, the running of the covering wire H₂ iscontrolled so that it meets the forming wire H₁ running on the formerroll further away than would be the case without said arrangement ofequipment. In this way the area of free draining on the face of theformer roll 11 is extended. A guide 20 is placed in each lateral area ofthe machine.

FIG. 4A is a more detailed illustration of the target area B₂ of theinvention shown in FIG. 3. FIG. 4B is a sectional view taken along theline II—II in FIG. 4A, and FIG. 4C illustrates the area B₃ in FIG. 4B inan enlarged scale. The rib 20 is connected with the bearing housing G₁of the former roll 11 or with the axle 11 a of the former roll 11 by theintermediate of a support arm 21. The arrangement is identical both atthe tending side and at the driving side of the machine. The seal 23 ispressed by means of a loading hose 26 with a pressure towards the rib 20in accordance with the invention so that the wire H₂ is pressed by theseal.

By means of a screw 25, the rib 20 can be positioned and attached to thefastening frame 22 connected with the support arm 21. The displaceableseal 23 is placed in a groove U in the upper frame 24, and the seal ispressed by means of a loading, hose 26 so that the covering wire H₂ isplaced against the face 20 a of the rib 20 and complies with its shape.

FIG. 4D is an enlarged illustration of the area B₃ in FIG. 4B.

FIG. 5A shows a solution of equipment 20 in accordance with theinvention in connection with a gap former in which the former roll 11has been substituted for by a water drain box (110).

The water drain box 110 can be a water drain box into whose interiorchamber a vacuum is applied, and so a suction is applied through the setof ribs on the water drain box further to the stock web, or the waterdrain box can also be a simple box construction provided with a set ofribs but with no inside vacuum.

FIG. 5B is a sectional view taken along the line III—III in FIG. 5A. Asis shown in FIG. 5B, the ribs 20 have been fitted at both sides of thesuction box 110, and they are supported on the suction box frame 111 bymeans of support arms 21. Thus, when the former. roll 11 is used, thesupport of the rib takes place by the intermediate of the support arms21, favourably on the axle 11 a or the bearing means G₁, G₂ of theformer roll 11, and, when the suction box 110 is used, the support ofthe ribs 20 takes place on the frame of the suction box.

The support and the sealing of the rib 20, both with a suction box 110and with a former roll 11, are similar to those shown in the embodimentsshown in earlier illustrations. Thus, also in the case of the formerroll 11, the covering wire H₂ is fitted to run so that the separate seal23 is pressed with the force of the loading hose against the coveringwire H₂ while the covering wire is placed between the top face 20 a ofthe rib 20 and the face of the seal 23, as is shown in FIG. 4C.

FIG. 6A shows the use of a rib 20 in accordance with the invention inconnection with a former which comprises a separate drain unit 115before the suction box 111 meant for water draining. Further, above thewire H₂, there is a suction box 112 intended for draining of water. Asis shown in the figure, in the twin-wire former shown in the figure, theforming wire H₁ is passed over the reversing roll E₁₀ from the vicinityof the headbox 100 over the suction boxes 115 and 111, which arepreferably ribbed suction boxes. Similarly, the forming wire H₂ ispassed over the reversing roll 12, so that, in the area in which theforming wires H₁ and H₂ reach contact with each other, a rib 20 inaccordance with the invention is used at the edges of the runs of theforming wires. From the headbox 100, the stock suspension is passed intoconnection with the forming wire H₁, along with which the stocksuspension moves, as is the case in the former embodiments, into the gapbetween the forming wires H₁ and H₂ and further to the scope of theeffect of the ribbed suction boxes 111 and 112, however, so that firstthe stock suspension is processed in connection with a pre-drain unit,i.e. with a ribbed suction box 115 as shown in the figure, before it ispassed to between the forming wires H₁ and H₂.

FIG. 6B is a sectional view taken along the line IV—IV in FIG. 6A. As isshown in FIG. 6B, ribs in accordance with the invention have been fittedin the lateral areas at both sides of the runs of the forming wires. Theconstruction. is similar to that shown in FIG. 4C, however, so that theformer roll is also in this embodiment substituted for by a ribbedsuction box 111. Thus, the present invention is suited for differenttwin-wire web formers.

What is claimed is:
 1. An equipment in a twin-wire former, in which apartly pre-drained or non-drained fibre stock is passed to between firstand second forming wires (H₁, H₂) of the web former in the vicinity ofthe former roll (11) or of a water drain box (110), in which connectionwater is drained out of the stock web by means of the former roll (11)or the water drain box (110), wherein the twin-wire former comprises: arib (20) in connection with the former roll (11) or the water drain box(110) in the lateral area of the wires (H₁ and H₂), which rib has beenfitted to control the running of the second forming wire (H₂) passedfrom a gap roll (12), and by means of which rib (20), in the lateralarea of the wire runs, the point at which said second forming wire (H₂)reaches contact with the first forming wire (H₁) in connection with theformer roll (11) or the water drain box (110) is shifted further away inthe machine direction, and that the rib (20) is an oblong structure,which has a maximal height (H_(max)) in the area between an inlet end(H_(in)) of the rib (20) and an outlet end (H_(out)) of the rib (20), inwhich case the thickness of the rib is increased when proceeding fromthe inlet end (H_(in)) of the rib to the position of maximal height(H_(max)) of the rib, and the thickness of the rib is lowered whenproceeding from the position of maximal height (H_(max)) of the rib tothe outlet end (H_(out)) of the rib.
 2. An equipment as claimed in claim1, wherein the height (H_(in)) of the rib at the inlet side is in arange of about 1 to 5 mm, and the height (H_(out)) of the rib at theoutlet side is in a range of about 1 to 5 mm, and that the maximalheight (H_(max)) of the rib in the middle area of the rib is in a rangeof about 5 to 30 mm.
 3. An equipment as claimed in claim 1, wherein thelocation of the rib (20) in the running direction of the wires is suchthat the starting point of the rib is at the earliest in the area (B₁)in which the wires reach contact with each other, and the end point ofthe rib is at the latest in an area in which the thickness of the web isless than 1 mm.
 4. An equipment as claimed in claim 1, wherein the rib(20) has been attached to a frame of the machine by means of screws (R₁;R₅), in which connection the position of the rib (20) in the machinedirection can be regulated by means of the screws (R₁).
 5. An equipmentas claimed in claim 1 wherein the rib (20) comprises: fastening means bywhose fastening means the position of the rib (20) in the crossdirection of the machine can be regulated.
 6. An equipment as claimed inclaim 1, wherein the rib (20) has been fitted to become narrower in thecross machine direction when proceeding in the running direction of thewire.
 7. An equipment as claimed in claim 1, wherein the rib (20) hasbeen fitted to become wider in the cross machine direction whenproceeding in the running direction of the wire.
 8. An equipment asclaimed in claim 1, wherein, in connection with the rib, there is a seal(23), which can be pressed with the pressure of one of an actuator and aloading hose (26), towards the rib (20) so that the forming wire (H₂)remains between the rib (20) and the seal (23).
 9. An equipment asclaimed in claim 8, wherein the loading hose (26) and the seal (23) havebeen fitted in a groove (U) in an upper frame (24), and the loading hoseand the seal (23) have been fitted substantially over the entire lengthof the rib (20).
 10. An equipment as claimed in claim 1, wherein theshape of the rib (20) can be varied so that the height of the rib (20)can be regulated by means of an actuator (70).
 11. An equipment asclaimed in claim 1, wherein the position/shape of the side face of therib (20) is regulated by means of an actuator (700).
 12. An equipment asclaimed in claim 8, wherein the actuators comprise loading hoses whichhave been fitted inside the rib (20).
 13. An equipment as claimed inclaim 1, wherein the ribs (20) have been supported by means of supportarms (21) on an axle (11 a) or bearings (G₁) of the former roll (11) orsupported on the frame (11) of the suction box.
 14. An equipment asclaimed in claim 1, wherein the twin-wire former is a gap former (10).15. A method in the regulation of a rib (20) which rib has been fittedto control the running of a second forming wire (H₂) passed from a gaproll (12), and by means of which rib (20), in the lateral area of thewire runs, the point at which said second forming wire (H₂) reachescontact with a first forming wire (H₁) in connection with a former roll(11) or a water drain box (110) is shifted further away in the machinedirection, and that the rib (20) is an oblong structure, which has amaximal height (H_(max)) in the area between an inlet end (H_(in)) ofthe rib (20) and an outlet end (H_(out)) of the rib (20), in which casethe thickness of the rib is increased when proceeding from the inlet end(H_(in)) of the rib to the position of maximal height (H_(max)) of therib, and the thickness of the rib is lowered when proceeding from theposition of maximal height (H_(max)) of the rib to the outlet end(H_(out)) of the rib, said method comprising the step of: altering aposition of one of a top face (20 a) of the rib (20) and a position of aside face (20 b) of the rib (20) by means of an actuator (70, 700).